The present invention relates to a triangle waveform generator having a comparator circuit which drives, via a limiter, an integrator, to the output of which is connected a first input of the comparator circuit and wherein the desired triangle waveform voltage is present at the output of the integrator.
Triangle waveform generators designed in this manner are commercially available. In the known arrangements, a comparator is followed by a flip-flop circuit which delivers a positive or negative voltage. The output of the flip-flop circuit is connected to a limiter comprising a resistor and a first diode coupled to a negative reference voltage source and a second diode coupled to a second reference voltage source having opposite polarity. A voltage is present at the output of the limiter which alternates between the positive and negative reference voltages, always in addition to the corresponding diode thresholds. This voltage, determined by the reference voltages, is then fed as an input voltage to an integrator. At a comparison input is present at one time a positive and at another time a negative comparison voltage by which the output voltage of the integrator and the switching point of the flip-flop circuit are fixed. This circuit is relatively expensive since, in addition to the comparator, a flip-flop circuit as well as a switching device for the comparison voltage of the comparator are required. Furthermore, due to differences in the threshold voltages of the two diodes connected to the reference voltages, complete symmetry of the triangular voltage cannot be achieved.
Further equipment is commercially available having triangle waveform generators in which the comparator circuit is directly followed by an integrator. The switching point of the comparison voltage for the rising and falling edges of the triangular voltage is realized by feeding back, in an operational amplifier acting as a comparator, the output via a resistor to the input. In such designs, however, the positive and negative slopes of the triangle waveform are not equal because the operational amplifier serving as the comparator goes into limit drive and then has different saturation voltages for positive and negative limit drive. Due to the difference in the voltages on the positive and negative side, the positive and negative peak values of the triangular voltage are also unequal. While they can be brought into agreement by a bias applied to the comparator, this necessitates trimming the circuit.
Examples of known arrangements for triangle waveform generators include U.S. Pat. Nos. 3,568,086 and 3,932,741.
It is, therefore, an object of the present invention to provide a triangle waveform generator wherein the output triangular voltage is completely symmetrical without the need for trimming circuitry.